The present invention relates to a bearing apparatus of a crankshaft for an internal combustion engine.
The crankshaft of a multi-cylinder internal combustion engine includes a plurality of journal portions and a plurality of crank pin portions. The plurality of journal portions includes a journal portion A (hereinafter referred to simply as “a journal portion A”) having a lubricating oil passage for supplying oil to the crank pin portions and a journal portion B (hereinafter referred to simply as “a journal portion B”) not having the lubricating oil passage. The crankshaft is supported in a lower part of a cylinder block of the internal combustion engine via a main bearing A in the journal portion A and via a main bearing B in the journal portion B. The main bearings A and B are formed into a cylindrical shape by assembling a pair of half bearings into a bearing holding hole of a bearing housing. The bearing housing includes an upper housing constituting a part of the cylinder block and a lower housing serving as a bearing cap. In order to lubricate the main bearings A and B, oil pumped by an oil pump is supplied into an oil groove formed along an inner peripheral surface of the main bearings A and B through an oil gallery formed in a wall of the cylinder block and through-holes formed in the walls of the main bearings A and B. The journal portion A includes a first lubricating oil passage formed through in a diameter direction of the journal portion A and the end openings thereof communicate with the oil groove of the main bearing A. Further, a second lubricating oil passage is formed branched from the first lubricating oil passage so as to pass through a crank arm portion and communicates with a third lubricating oil passage formed through in the diameter direction of the crank pin portion. Therefore, the oil supplied into the oil groove of the main bearing A passes through the first lubricating oil passage, the second lubricating oil passage, and the third lubricating oil passage, and then is supplied into a sliding surface between the crank pin portion and a connecting rod bearing from an end opening of the third lubricating oil passage (oil outlet formed in an outer peripheral surface of the crank pin portion).
The main bearing A and the main bearing B having the same shape are used. The oil groove is formed in an at least one of the inner peripheral surfaces of the pair of half bearings constituting the main bearing, and the oil groove is formed throughout the entire length in the circumferential direction of the half bearing (FIG. 1 in JP-A-08-277831). In this case, an amount of oil exceeding the amount necessary for lubricating the inner peripheral surface of the main bearing B is supplied.
Regarding the main bearing B, there is proposed a bearing apparatus which does not use an oil groove of the half bearing BU on the cylinder block side, but uses an oil hole formed through the inner peripheral surface and the outer peripheral surface of the half bearing BU, and causes oil externally supplied through the oil hole to flow into a clearance between the inner peripheral surface of the main bearing B and the surface of the journal portion B, thereby to reduce the amount of oil supplied to the main bearing B (WO-A-2004038188). Further, in the main bearing A of this bearing apparatus, the circumferential end portions of the oil groove formed along the circumferential direction of the inner peripheral surface of one half bearing AU do not communicate with a crash relief formed at the circumferential end portions of the inner peripheral surface of the half bearing AU. Thus, the partial structure of the oil groove of the half bearing AU suppresses oil in the oil groove from flowing outside of the main bearing A through a clearance caused by the crash relief. According to the bearing apparatus in WO-A-2004038188, the amount of oil supplied to the plurality of main bearings A and B of the bearing apparatus can be reduced, which can accordingly reduce the size of the oil pump and can reduce the fuel consumption of the internal combustion engine.
JP-A-2006-125565 has an object to overcome a drawback of the bearing apparatus (disclosed in FIG. 5) of WO-A-2004038188 that the main bearing B suffers from insufficient cooling and reduced durability. According to the bearing apparatus of JP-A-2006-125565, a partial oil groove is formed in the inner peripheral surface of one half bearing BU of the main bearing B, and this oil groove extends in the circumferential direction of the inner peripheral surface including the circumferential center position of the half bearing BU up to a little before the circumferential end portions (paragraph [0009]). This can increase the amount of oil supplied to the inner peripheral surface of the main bearing B, and thus can prevent reduction in durability of the main bearing B. Note that according to the main bearing A of the bearing apparatus of JP-A-2006-125565, the oil groove is formed throughout the entire length of the inner peripheral surface of one half bearing AU. The bearing apparatus of JP-A-2006-125565 increases the amount of oil supplied to the main bearing B, and thus requires an increase in size of the oil pump. The oil pump is operated by the rotating force of the crankshaft, and thus the increased size of the oil pump increases mechanical loss of the internal combustion engine.
Further, recent years have seen a tendency that an Al alloy is employed in the cylinder block to reduce the weight of the internal combustion engine for a passenger car. The bearing housing of the main bearing includes an Al alloy upper housing constituting a part of the cylinder block and an Fe alloy lower housing serving as the bearing cap. This bearing housing used for the bearing apparatus of JP-A-2006-125565 has a problem in that when the internal combustion engine is started (particularly when the internal combustion engine is started in a cold area where the bearing apparatus is in a low temperature state), oil is unlikely to be supplied into the sliding surface of the half bearing BL without an oil groove incorporated into the Fe alloy bearing cap side, thereby causing thermal seizure in the inner peripheral surface of the half bearing BL.
A bearing clearance for supplying oil is provided between the inner peripheral surface of the main bearing and the surface of the journal portion of the crankshaft. If this bearing clearance is too large, backlash is produced in the crankshaft, causing vibration and noise of the internal combustion engine. When the bearing housing includes the Al alloy upper housing and the Fe alloy lower housing, the bearing clearance is changed by a change in temperature due to a different thermal expansion coefficient of the journal portion between the Al alloy housing and the Fe alloy crankshaft. The bearing apparatus of the internal combustion engine for a passenger car is configured such that the bearing clearance is narrowed at a temperature (for example 120° C.) of the bearing housing during regular operation for quietness of the internal combustion engine. More specifically, the bearing clearance is changed such that the lower the temperature of the bearing housing, the bearing clearance is further narrower. The internal combustion engine for a passenger car is started in a cold area where the bearing housing is in a low temperature state (for example, about −30° C.). Thus, the difference in thermal expansion coefficient between the Al alloy housing and the Fe alloy crankshaft causes the bearing clearance to be extremely narrowed and further the oil viscosity is in a high state.
According to the bearing apparatus of JP-A-2006-125565, oil in the partial oil groove provided in the inner peripheral surface of the half bearing BU assembled into the Al alloy upper housing is in a high viscosity state, and further the bearing clearance between the inner peripheral surface of the half bearing BU and the surface of the journal portion is extremely narrow, and thus the oil is unlikely to flow from within the oil groove to outside. Therefore, the oil is not promptly supplied to the inner peripheral surface of the other half bearing BL assembled into the Fe alloy lower housing. For this reason, the inner peripheral surface of the other half bearing BL is damaged.